Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mcamelo on November 28, 2020, 04:47:45 pm

Title: Hammond OT for Plexi 6v6 build?
Post by: mcamelo on November 28, 2020, 04:47:45 pm
Hi, all.

I'm starting a Plexi 6v6 build and trying to find a suitable OT. Preferrably a Hammond since I can usually get them from Digikey delivered to Australia with free shipping (but open to alternatives).

I've found this one listed as suitable for 18W marshalls: https://au.mouser.com/ProductDetail/Hammond-Manufacturing/1750PA?qs=lrqjml%252Bjt8cxDhP5xJ0Rrw%3D%3D (https://au.mouser.com/ProductDetail/Hammond-Manufacturing/1750PA?qs=lrqjml%252Bjt8cxDhP5xJ0Rrw%3D%3D)  but I'm not sure how well it suits the Plexi 6v6.

I can't yet on my own calculate the tubes power output or OT primary impedance from the schematics. If anyone can tell me what they are, I could use that to go shopping for a suitable OT.

:help:

Any pointers will be greatly appreciated.     
Title: Re: Hammond OT for Plexi 6v6 build?
Post by: shooter on November 28, 2020, 05:07:54 pm
you calculate based on operating conditions, not schematic, or look at a tube datasheet and aim for a specific set of spec's.
that said the one you referenced appears fine
Title: Re: Hammond OT for Plexi 6v6 build?
Post by: vampwizzard on November 28, 2020, 08:32:59 pm
Should be good. MHuss used an 18 watt spec'ed for his build.
Title: Re: Hammond OT for Plexi 6v6 build?
Post by: AmberB on November 28, 2020, 11:23:51 pm
It looks like that OT is rated at 8.4k secondary and 18 watts output, so it should work well for a pair of 6V6s...
Title: Re: Hammond OT for Plexi 6v6 build?
Post by: Latole on November 29, 2020, 03:39:15 am
Quote from: AmberB on November 28, 2020, 11:23:51 pm
It looks like that OT is rated at 8.4k secondary and 18 watts output, so it should work well for a pair of 6V6s...

Primary not secondary  :laugh:

mcamelo, OT will work
Title: Re: Hammond OT for Plexi 6v6 build?
Post by: pdf64 on November 29, 2020, 03:45:48 am
It seems a quirk of guitar amp evolution that only the high power models were deemed worthy of OTs with a decent spec. I suggest to consider something beefier, interleaved for better performance, more akin to a 784-139.
Unfortunately I’m not aware of anything with an 8k primary that meets that criteria other than OT intended for JTM45, eg 1750Q, which is way more expensive.
EDIT Another option would be the hifi 25W 1650FA but that’s even more pricey.
Title: Re: Hammond OT for Plexi 6v6 build?
Post by: DummyLoad on November 29, 2020, 04:50:14 am

1750E
1760E
1750F
1760F
1750FA
1750PA


are all suitable parts in the hammond line.


--pete
Title: Re: Hammond OT for Plexi 6v6 build?
Post by: mcamelo on November 29, 2020, 02:55:05 pm
Quote from: shooter on November 28, 2020, 05:07:54 pm
you calculate based on operating conditions, not schematic. look at a tube datasheet and aim for a specific set of spec's.

I was thinking it was the circuit design that determined the operating conditions by setting the plate, cathode and grid's idle currents but, looking at the Tung-Sol 6v6 datasheet, I now see that it lists typical operating conditions. Makes sense.

Quote from: shooter
the one you referenced appears fine

Thank you and everyone else that chimed in with guidance.
I will look at all the options and comeback with more questions if I have any.